The use of computers having both a video monitor and a keyboard to input and display information are quite common. Many homes have what is typically referred to as a personal computer or a home computer. Home video games are also quite common, as are video arcade games. Most of the foregoing depend upon locating an image (i.e. cursor) on a screen in order to perform a specific function. For example, in what is frequently called a computer typewriter, a cursor is moved on a screen to indicate the location at which a correction is to be made. The cursor may also be used to select a particular mode of operation. A cursor may be moved to draw lines on a screen, commonly called a video display tube. In many of the foregoing, the keyboard is used to provide information to the computer. In some of these applications, swiftness, speed and accuracy are very desirable. For example, in a computer typewriter, the typist generally is trying to type words as fast as possible. Such typing will be displayed on the screen of a video monitor. The typist will try to make corrections as quickly as possible by moving the cursor around the screen.
In the prior art, the cursor movement is accomplished by a device commonly called a mouse. The mouse generally has the shape of a spherical ball which protrudes through the bottom of a housing. Pushing on the mouse will cause the ball to rotate, which in turn will cause an image on the screen to move. The mouse has no inherent up, down, left or right sense of direction, since it is a sphere and can be rotated in any direction. This makes the mouse very difficult to use in a typing situation where the typist is attempting to type as fast as possible while looking at a screen without looking at the mouse. The typist would have to move the mouse in several directions before finally positioning the cursor at the desired coordinates on the screen. Other prior art devices used in computer typewriters include buttons that can be pushed to cause movement of the cursor. For example, one button could be pushed to provide up direction while another button could be pushed to provide down direction, and so forth. The use of bottons does not allow the typist to speed up the process since the movement of the cursor will be either constant or depend on tapping of the button.
Another prior art device for controlling a cursor on a screen is a joy stick that protrudes up from a base. The joy stick is generally moved forward to cause the cursor to move up. The stick is moved to the side to cause the cursor to move to the side, as is commonly done with many home video games.
All of the prior art devices that control the position of an image on a screen are inconvenient to use because, they are remotely located from the keyboard. In particular, where one wishes to draw on a screen, such as a video display tube, by using a cursor as the point of reference, it is very difficult to use a mouse to draw a straight line, because it is difficult to cause a sphere to move in a straight line. It is equally difficult to draw a precise distance using a joy stick or a pushbutton, because one must estimate for how long the stick must be moved to cause a corresponding movement of the cursor for how long the button must be pushed to cause the movement desired. Consequently, it is almost impossible to precisely draw a line of desired length.
Thus, there are positioning systems in the prior art for positioning images on a screen. However, each has obvious disadvantages which are overcome by the invention to be described in this patent application.